In this paper, we tackle two problems related to the orthogonal Multiple Access Multiple Relay Network (MAMRN): the Rate Allocation (RA) problem, and the relaying nodes Scheduling Strategy (SS). The RA consists in choosing a rate for each source. The SS consists in organizing the retransmission phase where some relaying nodes are activated to help some sources. The destination is the central node that schedules the rates of the sources and the cooperative retransmissions of the relaying nodes. We propose solving the two problems (i.e., the RA and the SS problems) jointly contrary to the prior art where the solution is done separately. We aim to remove the sub-optimality of solving the two problems non-jointly, leading to the optimal strategy that gives the highest spectral efficiency.